There is at the present time a significant medical need for new anti-inflammatory and anti-arthritic drugs with reduced side effects and prolonged in vivo activity and in particular for compounds which will moderate the progress of the arthropathies. Plants and other living cells offer a vast reservoir of compounds which have pharmacological effects on humans. Natural products have frequently been the source of effective drugs and lately there has been an increased interest in the analysis of these natural products, especially where a clinical benefit is claimed. Marine organisms contain metabolites that can act as pharmacological agents and aid in the treatment of inflammation.
An anti-inflammatory activity of Perna canaliculus (New Zealand Green Lipped Mussel) was first implicated as part of a pharmacological study on leukaemia. Initial assessment of the anti-inflammatory activity of Perna canaliculus was first attempted using a polyarthritis model in rats.sup.1. These studies however failed to show the presence of any significant anti-inflammatory activity in the mussel preparation. In contrast, Miller and Ormrod.sup.2 using a carrageenin-induced paw oedema assay.sup.3, were able to show that mussel preparations, when administered intraperitoneally, gave a significant reduction in the swelling of a carrageenin-induced rat paw oedema. Subsequently, they fractionated a non-dialysable, water-soluble fraction from the mussel preparation that possessed anti-inflammatory activity. The aqueous extract showed a dose-dependent anti-inflammatory activity when administered intraperitoneally and could pot be detected upon oral administration of the mussel powder. It was suggested that the water-soluble fraction therefore contained an irritant component possessing apparent anti-inflammatory activity.
Rainsford and Whitehouse.sup.4 also reported that freeze-dried powdered preparations of the whole mussel given orally to rats showed some modest anti-inflammatory activity in the carrageenin-induced paw oedema assay, and that this material strikingly reduced the gastric ulcerogenicity of several non-steroidal anti-inflammatory drugs in rats and pigs.
Use of the whole mussel extract in the treatment of both rheumatoid arthritis and osteoarthritis in human patients has also been reported.sup.5.
Initial work leading to the present invention based on lipid extracts from Perna canaliculus powder prepared using solvent extraction techniques (in contrast to earlier work on aqueous fractions), established that the lipid fractions show a measure of anti-inflammatory activity when tested in appropriate model systems. A reliable source of lipid extract of Perna canaliculus and Mytilus edulis has subsequently become available through the procedure of supercritical fluid extraction (SFE). The lipid extract is obtained as a dark yellow-brown viscous oil exhibiting strong ultraviolet absorbing character which is consistent in physical data to lipid extracts obtained from earlier solvent extraction procedures.